Why Peptides Weren't in Your Medical Training (And Why That's Changing)

A patient arrives on tirzepatide, having lost twenty kilograms. She wants to know whether she should also be taking BPC-157, which her trainer recommends, and whether the sermorelin she found online is comparable to growth hormone. These are three distinct questions with three distinct answers, and most physicians were never given a framework for any of them.

That gap is not a failure of individual training. It is the predictable result of how pharmacology has been taught for fifty years, colliding with a category of drugs that changed faster than any curriculum could absorb.

What was actually taught

Peptides were never absent from medical school. Insulin was covered exhaustively. Oxytocin appeared in obstetrics, GnRH agonists in oncology and reproductive endocrinology, octreotide in gastroenterology, desmopressin in nephrology, calcitonin and teriparatide somewhere near the osteoporosis lecture.

What was missing was the connective tissue. Each of these appeared as a hormone within an organ system, taught by the specialist who used it, rather than as a member of a class with shared pharmacological properties. A graduate could describe leuprolide's effect on the pituitary without recognising that it, semaglutide and teriparatide share a mechanism of action, a formulation problem and a clearance profile.

Pharmacology curricula are organised around receptor families and small-molecule drug classes because that organisation works for most of the formulary. Beta blockers behave like beta blockers. Peptides, distributed one at a time across nine organ systems, never accumulated into a chapter. There was no point at which a student was told: these molecules are related, and here is what they have in common.

Why the category stayed small

For most of the twentieth century, that filing decision was defensible, because there were very few peptide drugs to teach. Three constraints kept the category small, and all three were chemical rather than clinical.

The first was manufacturing. Insulin, the first peptide drug, was extracted from bovine and porcine pancreas beginning in 1922. Producing a peptide meant obtaining it from animal tissue, which limited supply, purity and the range of molecules available. Chemical synthesis arrived in 1954 with du Vigneaud's total synthesis of oxytocin and vasopressin, recognised with the Nobel Prize in Chemistry the following year, but solution-phase methods were slow and low-yielding. The decisive change was Merrifield's invention of solid-phase peptide synthesis in 1963, which made assembly automatable and eventually industrial. [1]

Recombinant production in the 1980s extended the same logic to larger molecules.

The second constraint was pharmacokinetics. Native peptides are cleared in minutes. Endogenous GLP-1 has a circulating half-life of roughly two minutes because dipeptidyl peptidase-4 cleaves it almost immediately. A signalling molecule designed to be transient makes a poor drug, and until that could be engineered around, most peptides were undruggable regardless of how well their biology was understood.

The third was route. Peptides are protease substrates that cross membranes poorly, which meant injection, which meant limited uptake outside conditions serious enough to justify it.

Solving those problems took forty years of chemistry: sequence substitution to block enzymatic cleavage, fatty-acid acylation and PEGylation to promote albumin binding and slow renal clearance, and eventually absorption enhancers for oral delivery. None of this work happened in medical schools, and none of it generated the kind of clinical trial results that force curriculum revision. It accumulated quietly in medicinal chemistry until it produced something the clinical world could not ignore.

The curriculum problem is structural

Even had someone wanted to add a peptide pharmacology block, the space did not exist.

Pharmacology content expands continuously while undergraduate teaching hours do not, and the discipline has been openly discussing the resulting squeeze for years. [2]

The shift from discipline-based teaching to integration across clinical years, intended to make pharmacology more contextual, had the side effect of reducing its visibility as a subject in its own right. A recent analysis of one UK medical programme found that students were introduced to more than a thousand drugs or drug classes in their first two years alone and reported feeling overwhelmed. [3]

Under those conditions, new material enters the curriculum with a substantial lag, and the lag is longest for content that does not map cleanly onto a single organ system or a single examination topic. Peptides are precisely that kind of content. The consequence is that a physician who graduated in 2015 received essentially the same peptide teaching as one who graduated in 1995, despite the intervening decade having transformed the category.

What changed

The engineering succeeded, and then the market did.

Roughly 12% of US adults report currently taking a GLP-1 receptor agonist and 18% report having taken one at some point. [4]

Separate polling focused specifically on weight loss found current use rising to about 11% in 2026, up from 3% two years earlier. [5]

Among adults with diagnosed diabetes, more than half report having used one; among those with heart disease, around four in ten.

Those figures matter for reasons beyond obesity medicine. A drug class taken by one in eight adults appears in every preoperative assessment, every medication reconciliation, every pregnancy consultation and every gastroenterology referral. Anaesthesia has already had to revise fasting guidance because of delayed gastric emptying. This is no longer an endocrinology topic that a generalist can reasonably defer.

The category is also no longer confined to injections. A small-molecule oral GLP-1 receptor agonist has now reached approval, which will accelerate uptake further and blur the boundary between peptide therapeutics and conventional pharmacology in a way that makes the class-based framework more useful, not less.

The second gap

The harder problem is the one the curriculum could never have anticipated: patients arrive already taking peptides that are not approved for anything.

BPC-157, ipamorelin, CJC-1295, thymosin alpha-1 and their relatives circulate through wellness clinics, telehealth platforms and online vendors. The regulatory position on them has been unstable — the FDA moved 19 such substances to Category 2 of the 503A bulks list in late 2023, restricting them from compounding, and in July 2026 an advisory committee narrowly recommended six of them for reinstatement, against the written advice of the agency's own reviewers. That process is still incomplete, and none of these substances is FDA approved.

A physician confronting this needs to hold several things at once: that the underlying receptor biology is often real, that real biology does not establish clinical benefit, that a compounded product's identity and purity may be unverifiable, and that a patient who feels dismissed will simply stop disclosing. None of that is difficult reasoning. It is just reasoning nobody was taught to apply to this particular category.

Where the education is actually coming from

Here the honest assessment is uncomfortable. Undergraduate medical education has not closed this gap and shows little sign of doing so quickly. Most peptide education now reaching practising physicians arrives through continuing medical education, specialty societies, conference faculty and training programmes with varying degrees of commercial entanglement.

Some of that instruction is rigorous. Some of it is marketing with a lecture format. The distinction is not always obvious from the outside, and physicians evaluating these programmes should apply the same scrutiny they would apply to any industry-sponsored education: who funds it, whether the faculty disclose relationships with the products discussed, whether unapproved uses are clearly identified as unapproved, and whether the evidence presented includes negative and null findings.

The uncomfortable corollary is that a field's education being delivered largely by its enthusiasts is a structural risk regardless of any individual's integrity.

What a clinician actually needs

Not a specialty. A framework, and it is short.

Know where the peptide/protein boundary falls and why it determines regulatory pathway, because that single distinction sorts the category into approved drugs and everything else. Know the difference between replacing a signal and prompting endogenous production, because secretagogues and recombinant hormones are not interchangeable. Ask about half-life and formulation before accepting that two products with the same target are equivalent. Ask where a compounded product was sourced and whether identity and purity can be documented. Ask what the patient is already taking, in a manner that makes honest disclosure likely.

That is a defensible working knowledge, and it is achievable in an afternoon. The barrier was never difficulty. It was that no one ever put the pieces in the same place.

For the underlying pharmacology, see the companion primer: What are peptides? A clinician's primer on peptide vs protein signalling.